The present invention relates to a device and a method for testing the seal tightness of a fuel tank system of a motor vehicle. More particularly, the present invention relates to a device and method in which excess pressure (or low pressure) is created in the tank system by an electrically operated pump, the electric current consumption of the pump is compared to reference values in order to determine whether the seal tightness of the tank system is sufficient, and the tank system includes a filler neck that can be closed with a fuel tank cap. By way of example, reference is made to the prior state of the art such as DE 195 02 775 C1.
As is generally known, in some countries legal regulations are in place, according to which the fuel tank system of motor vehicles must be checked onboard for tightness on a regular basis. Mostly after turning off the vehicle, a certain excess pressure is created in the fuel tank by means of an electrically operated air pump and the required electric current is measured. The pump or the measurement instrument is calibrated prior to the measurement, based on the current consumption that is experienced when guiding a reference leakage current through an air outlet opening that has been standardized in terms of its size. If, during the proper measuring process, the electric current consumption is within a certain range of values, the conclusion can be drawn that the tank system is adequately tight. If, however, the electric current consumption is noticeably lower, this is an indication of leakage in the tank system.
Leakage is also detected with the measurement instrument in cases in which an ordinary fuel tank cap closing the typical filler neck is not properly attached or screwed on, and, therefore, the filler neck is not properly closed. Although simple manual tightening would suffice to correct this problem, typically, a warning signal is activated, which requires the driver of the vehicle to visit the closest automotive repair shop in order to have the problem of the alleged leaking tank system corrected.
In order to remedy the above-described problem, an electric switch can be provided on, or working with, the fuel tank cap. Based on the state of the switch, a conclusion may be drawn as to whether the filler neck is closed properly or is at least partly open. Using an electronic control unit, with which the entire tightness test is controlled, would then allow the respective signal of this fuel tank cap switch to be suitably considered and the vehicle driver to be informed accordingly. Alternatively, the vehicle driver can be alerted to the fact that the fuel tank cap has not been closed properly, and, therefore, the filler neck is not closed completely. However, in order to implement this possible solution, an electric signal line leading from the tank cap or, more precisely, from the tank cap switch to this electronic control unit is required, as well as a corresponding input for the electric signal line on the control unit.
Since this is relatively expensive to do, the present invention provides a simplified device and a corresponding method for testing the seal tightness of a fuel tank system of a motor vehicle, wherein, by means of an electrically operated pump, excess pressure is built up in the tank system and the electric current consumption of the pump is compared to reference values in order to determine whether the tightness of the tank system is sufficient, and wherein the tank system includes a filler neck with a locking fuel tank cap.
In exemplary embodiments of the present invention, a control line is connected in parallel to the power supply line of the pump, the line being guided across an electric tank cap switch, which assumes a different switch position when the filler neck is closed properly than when the filler neck is not closed properly. In at least one of these lines, an electric resistor is installed such that, when the filler neck is not closed properly and the pump is set in operation, an electric current develops in the two lines, which allows a conclusion to be drawn on the respective switch state of the tank cap switch.
Using this suggestion, the electric current conducted to the pump, or, more precisely, to the electric driving motor thereof, is modified as a function of the switch state, where applicable. Specifically, in the case of suitable selection of the aforementioned electric resistor, the current flow, which can be detected or measured when the filler neck has not been closed properly, is outside the current value range typically consumed by the pump or the driving motor thereof.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.